"Scripture often asserts that man is the slave of sin. What it means is that his mind is so far removed from God's righteousness that he thinks of, deeply desires and undertakes nothing that is not evil, perverse, iniquitous and sullied; for the heart, having drunk its fill of sin's venom, can emit nothing but sin's fruits.
However, we must not think that there is some violent necessity driving man to sin. He sins with the full agreement of his own will, and he does it eagerly and in line with his own inclinations.
The corruption of his heart means that man has a very strong and continuing hatred of the whole of God's righteousness. In addition, he is devoted to every kind of evil. Because of this he is said not to have the free power of choosing between good and evil - which is called free will."
- John Calvin, Truth For All Time